1. Field of the Invention
The invention relates to a light source device using a high pressure mercury discharge lamp which is used, for example, as a light source for a projector.
2. Description of the Prior Art
In a light source device for an optical device, such as a liquid crystal projector, a DLP(copyright) projector (Texas Instruments) or the like, a discharge lamp with high radiance (HID lamp) is used. However, recently, more and more often there has been a need for a larger amount of mercury to be added to the discharge lamp than in the conventional case, in order to make the above described optical device more radiant.
Furthermore, since the degree of utilization of the light emitted from the discharge lamp becomes greater, the more the light source approaches a point light source, there is more and more a demand for reducing the distance between the electrodes of the discharge lamp in order to make the discharge emission area of the lamp smaller.
However, if the amount of mercury to be added is increased and the distance between the electrodes is reduced, the phenomena occurs that, when the lamp is turned off and when the temperature drops as a result, the vaporized mercury condenses on the electrodes as liquid and the gap between the electrodes, as the two poles, is bridged, or there is the phenomenon that the mercury, due to vibration during transport of the device or the like, enters the gap between the electrodes and bridges it even if the mercury has not been liquified by condensation.
When this phenomenon occurs, the gap between the electrode is short-circuited by the mercury. Therefore, there is the disadvantage that a discharge cannot occur between the electrodes and that the lamp can no longer be operated. If the feed device does not have a protective function against the current exceeding a certain value, there is also the disadvantage that the feed device is damaged due to the current exceeding a certain value.
In the case of a feed device with a protective function against the current exceeding a certain value, damage is prevented. However, since the operator of the device cannot know that such a phenomenon has occurred, there is the disadvantage that the device is considered defective even if the device can be used in practice by eliminating the bridging short circuit by eliminating the mercury which is bridging the gap between the electrodes by gently striking the lamp or the device.
A primary object of the present invention is to eliminate the disadvantage that exists in the prior art that it cannot be determined whether or not a light source device with a mercury lamp is defective when a bridging short circuit of the gap between the electrodes of the discharge lamp is caused by mercury, so that the light source device can no longer be used once such occurs.
In a first aspect of the invention, in a light source device in which the following components are connected to one another:
a discharge lamp in which a pair of electrodes are arranged oppositely; and
a feed device for supplying a discharge current to the electrodes for the main discharge;
the object is achieved in that the light source device has the following functions:
the function of determining that a bridging short circuit in the gap between the electrodes of the discharge lamp by mercury has occurred; and
the function of displaying that the formation of a bridging short circuit by the mercury has occurred.
In a second aspect of the invention, in a light source device in which the following components are connected to one another;
a discharge lamp in which a pair of electrodes are arranged oppositely; and
a feed device for supplying a discharge current to the electrodes for the main discharge;
the object is achieved in that the light source device has the function of determining the occurrence of a bridging short circuit in the gap between the electrodes of the discharge lamp by mercury and that the light source device has a means for eliminating the bridging short circuit which is used to eliminate the bridging short circuit caused by the mercury.
The object is achieved in a development of the invention in that, in the version according to the second aspect of the invention, the means for eliminating the bridging short circuit is a means which applies a vibration or an impact to the discharge lamp.
The object is furthermore achieved preferably in that, in the version according to the second aspect of the invention, the means for eliminating the bridging short circuit is a means which heats the lamp.
The object is moreover feasibly achieved in that, in the invention described in the paragraph above, in the means for eliminating the bridging short circuit, there is an auxiliary electrode in addition to the electrodes for the main discharge, so that a discharge can form between the auxiliary electrode and one of the electrodes for the main discharge.
The object is advantageously achieved furthermore in that, in the version according to the second aspect of the invention, the means for eliminating the bridging short circuit applies a magnetic field to the gap between the electrodes, and moreover, supplies a current to the mercury which is causing the bridging short circuit and that, in this way, the mercury which causes the bridging short circuit is moved by a Lorentz force which acts on the mercury.
The invention is further described below using several embodiments shown in the drawings.